#4184: Squirrelly inliner behaviour leads to 80x slowdown
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Reporter: bos | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.12.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
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Description changed by igloo:
Old description:
> Recently, I switched the mwc-random package
> (http://hackage.haskell.org/package/mwc-random) over from running in the
> ST monad to using Roman's primitive package. I didn't notice initially,
> but this caused a huge performance regression.
>
> mwc-random 0.4.1.1 uses ST internally, and runs the benchmarks/Quickie
> benchmark in 0.017 seconds.
>
> mwc-random 0.5.1.3 uses PrimMonad internally, and takes 1.328 seconds to
> run the same benchmark.
>
> That's about a factor of 80 slowdown. This causes a massive knock-on
> performance loss in packages such as criterion that need fast PRNGs.
>
> The problem is very easy to reproduce:
>
> cabal install mwc-random-0.4.1.1
> cabal install mwc-random-0.5.1.3
> darcs get http://darcs.serpentine.com/mwc-random/
> cd mwc-random/benchmarks
> ghc -fforce-recomp -O -package mwc-random-0.4.1.1 --make Quickie -o
> quickie-411
> ghc -fforce-recomp -O -package mwc-random-0.5.1.3 --make Quickie -o
> quickie-513
>
> time ./quickie-411
> time ./quickie-513
New description:
Recently, I switched the mwc-random package
(http://hackage.haskell.org/package/mwc-random) over from running in the
ST monad to using Roman's primitive package. I didn't notice initially,
but this caused a huge performance regression.
mwc-random 0.4.1.1 uses ST internally, and runs the benchmarks/Quickie
benchmark in 0.017 seconds.
mwc-random 0.5.1.3 uses PrimMonad internally, and takes 1.328 seconds to
run the same benchmark.
That's about a factor of 80 slowdown. This causes a massive knock-on
performance loss in packages such as criterion that need fast PRNGs.
The problem is very easy to reproduce:
{{{
cabal install mwc-random-0.4.1.1
cabal install mwc-random-0.5.1.3
darcs get http://darcs.serpentine.com/mwc-random/
cd mwc-random/benchmarks
ghc -fforce-recomp -O -package mwc-random-0.4.1.1 --make Quickie -o
quickie-411
ghc -fforce-recomp -O -package mwc-random-0.5.1.3 --make Quickie -o
quickie-513
time ./quickie-411
time ./quickie-513
}}}
--
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4184#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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